1. Field of the Invention
The present invention relates to a shift control method and system of a hybrid vehicle. More particularly, the present invention relates to a shift control method and system of a hybrid vehicle that prevent engine clutch slip from occurring when a transfer torque of engine clutch is greater than an allowable transfer torque under unfavorable driving conditions by controlling a shifting time.
2. Description of Related Art
As is generally known in the art, a hybrid vehicle uses an internal combustion engine and a battery power supply together. That is, the hybrid vehicle efficiently combines power of the internal combustion engine and power of a driving motor for use.
As illustrated in FIG. 1, the hybrid vehicle may include, for example, an engine 10, a driving motor 20, an engine clutch 30 for intermitting between power between the engine 10 and the driving motor 20, a transmission 40, a differential gear device 50, a battery 60, an integrated starter-generator 70 for starting the engine 10 or generating electricity by rotational force of the engine 10, and vehicle wheels 80.
Furthermore, the hybrid vehicle may include a hybrid control unit (HCU) 200 for controlling an entire operation of the hybrid vehicle. an engine control unit (ECU) 110 for controlling an operation of the engine 10. a motor control unit (MCU) 120 for controlling an operation of the driving motor 20. a transmission control unit (TCU) 140 for controlling an operation of the transmission 40. a battery control unit (BCU) 160 for controlling and managing the battery 60.
The battery control unit 160 may be called a battery management system (BMS). The integrated starter-generator 70 may be called an integrated starter & generator (ISG), or a hybrid starter & generator (HSG).
The hybrid vehicle may be driven in a driving mode such as an electric vehicle (EV) mode which is a true electric vehicle mode using only power of the driving motor 20, a hybrid vehicle (HEV) mode which uses rotational force of the engine 10 as main power and uses rotational force of the driving motor 20 as auxiliary power, and a regenerative braking (RB) mode for collecting braking and inertial energy during driving by braking or inertia of the vehicle through electric generation of the driving motor 20 to charge the battery 60.
The hybrid vehicle may use a dry-type engine clutch, and the dry-type engine clutch should be maintained fully closed condition while shifting. Therefore, an allowable transfer torque of the dry-type engine clutch may be determined by a motor, a rotational inertia of the engine, an angular acceleration, and an engine torque.
However, engine clutch slip may occur because a transfer torque is greater than an allowable transfer torque when the hybrid vehicle is operated under unfavorable driving conditions. For example, the engine clutch slip may occur when the hybrid vehicle is operated at an extremely low temperature or the hybrid vehicle shifts according to an additional torque of the engine.
That is, when the hybrid vehicle is operated under unfavorable conditions, the engine clutch slip may occur due to a difference of rotational inertia between the motor and the engine that is generated when the transfer torque is greater than the allowable transfer torque during shifting. when such an engine clutch slip occurs, the hybrid vehicle is negatively influenced with regard to shifting safety, vehicle vibration, and fuel consumption.
In order to prevent the aforementioned problem, the allowable transfer torque of the engine clutch is increased, but the size of the engine clutch and a secure space for installing it need to increase.
The information disclosed in this Background of the Invention section is only for enhancement of understanding of the general background of the invention and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art already known to a person skilled in the art.